1. Field of the Invention
The present invention relates to a vibration damping mount assembly composed of a tubular bracket attached to a mounting main body which is employed as an engine mount in an automobile or the like.
2. Description of the Related Art
As one type of vibration damping couplings or vibration damping supports for installation interposed between components making up a vibration transmission system, there is known a vibration damping mount of a structure in which a first mounting member is positioned spaced apart from the opening at one axial end of a tubular second mounting member, with the first mounting member and the second mounting member being elastically connected by a main rubber elastic body. Such vibration damping mounts are suitable for use as engine mounts in automobiles, for example.
For reasons pertaining to the manufacturing process or the like, vibration damping mounts having the above described structure are sometimes designed so that the second mounting member is attached via a bracket to the vehicle body or other component to be connected in vibration-damping fashion. Specifically, where for example a certain extent of pre-compression is applied to the main rubber elastic body in order to enhance the durability of main rubber elastic body, one known method involves subjecting the second mounting member to a diameter-reduction process such as crimping from all directions. Where such a diameter-reduction process is carried out, if the attachment member to the component to be connected in vibration-damping fashion has been disposed directly on the second mounting member, it tends to be difficult to carry out diameter-reduction of the second mounting member in a satisfactory manner. To cope with this drawback, typically the second mounting member is press-fit into a separately formed tubular bracket and then the tubular bracket is fastened to the vehicle body or other component to be connected in vibration-damped fashion, whereby the second mounting member is attached to the component in a vibration damping fashion via the tubular bracket (as shown in U.S. Pat. No. 6,325,364, for example).
In order to prevent deformation or breakage of the tubular bracket due to the vibration damping mount main body being press-fit into the tubular bracket, conventional tubular brackets are typically formed of ferric metals which readily afford high levels of rigidity. However, in order to meet recent tendency to improve mileage and lighter weight of vehicles, extensive research has been made as to the use of aluminum alloys and other non-ferric metals or synthetic resin materials such as fiber-reinforced plastic as materials for forming the tubular bracket.
Where the tubular bracket has been fabricated of lightweight material such as non-ferric metal or synthetic resin, it is typically difficult to achieve satisfactory levels of load-bearing strength, as compared with a tubular bracket made of ferric metal. A resultant problem was that the tubular bracket tended to experience cracking during press-fitting of the second mounting member into a tubular bracket made of lightweight material. Another problem was that if the tubular bracket was made thick enough to ensure satisfactory load-bearing strength, the advantage of making the tubular bracket from lightweight material was defeated so that sufficient weight reduction of the tubular bracket was not achieved.
The present applicant has been proposed in JP-A-2005-106150 a vibration damping mount assembly adapted to avoid damage to a tubular bracket made of lightweight material such as non-ferric metal or synthetic resin during assembly of the vibration damping mount with the tubular bracket. Specifically, the vibration damping mount assembly taught in JP-A-2005-106150 has a structure in which the second mounting member of the vibration damping mount main body is fitted within a tubular bracket made of lightweight material with a gap present therebetween; and a rubber coupler in a compressed state is then interposed in the gap between the second mounting member and the tubular bracket, fixedly positioning the vibration damping mount main body and the tubular bracket. With this arrangement, the second mounting member is fit into the tubular bracket with a gap therebetween, so that it is possible to avoid damage to the tubular bracket due to pressing force during press-fitting of the second mounting member caused in the conventional structure.
However, further research conducted by the inventors has shown that, even with the structure taught in JP-A-2005-106150, there is clearly room for further improvement.
Specifically, with the vibration damping mount assembly disclosed in JP-A-2005-106150, the rubber coupler made of a rubber elastic body is interposed between the second mounting member and the tubular bracket, and the second mounting member is pushed and fitted into the tubular bracket in such a way that the rubber coupler is compressed between them. Accordingly there is a risk that after the second mounting member has been fitted within the tubular bracket, when the rubber coupler is subjected to shear deformation in the axial direction, its resilience will give rise to force acting on the vibration damping mount main body in a direction dislodging it from the tubular bracket (dislodging force), causing the vibration damping mount main body to undergo displacement relative to the tubular bracket. There is a consequent risk of the vibration damping mount main body experiencing shifting out of position relative to the tubular bracket; and in some instances the force of resistance of the vibration damping mount main body to becoming dislodged from the tubular bracket may not be sufficient to avoid the risk of the vibration damping mount main body falling out from the tubular bracket.
Moreover, the vibration damping mount assembly disclosed in JP-A-2005-106150 is designed so that frictional force produced between the tubular bracket and the rubber coupler may be utilized to create force of resistance to dislodging in order to prevent the vibration damping mount main body from becoming dislodged from the tubular bracket. Thus, in order to obtain a sufficient level of resistance to dislodging force, it will be necessary to ensure a sufficient level of compressive deformation of the rubber coupler, in other words, of perpendicular resistance acting on the rubber coupler. However, where the compressive deformation of the rubber coupler is sufficiently great, that fitting the vibration damping mount main body into the tubular bracket will become difficult. Even where the vibration damping mount main body and the tubular bracket are positioned together by fastening the vibration damping mount main body and the tubular bracket together with a bolt or the like as taught in JP-A-2005-106150, it was difficult in some instances to assemble the vibration damping mount main body so that it fits into the tubular bracket at the prescribed location.